This invention relates to a process of producing carbon particles and/or deposits, and more particularly to the simplified preparation of dense carbon having properties approaching those of commercial-grade diamond particles. These high density carbons are grouped under the term metastable carbon phases and generally have a density greater than 2.26 g/cm.sup.3. Products termed "metastable carbon phases" typically include diamond, lonsdaleite (or hexagonal diamond), chaoite and carbon VI (sometimes called white carbon), .alpha.-carbyne and .beta.-carbyne.
In the past, the high density carbon phases have been formed by using unusual temperatures and/or pressures. For example, vitreous carbon heated to 2000.degree.-3000.degree. C. during manufacture was shown to contain such products. In still other work, graphitic carbon was heated above 2300.degree. C. in a range of 10.sup.-4 Torr to 1 atmosphere to produce carbon VI. Chaoite was produced during graphite sublimation at 2400.degree.-2700.degree. C. and 10.sup.-4 Torr. Lonsdaleite has been produced with a static pressure exceeding 130 Kbar and a temperature greater than 1000.degree. C.
Diamond can be produced at 130 Kbar and 3000.degree. C.; or, with Ni or Fe catalysts, at 27 Kbar and 1400.degree. C. Additionally, shock-wave synthesis of diamond from 0.3 to 1.5 Mbar at about 1000.degree.-2000.degree. C. has been utilized. In other work, diamond or diamond-like carbon has been produced by ion beam deposition from a plasma at 10.sup.-3 to 10.sup.-6 Torr with high voltage, e.g., 40 V or about several thousand degrees. Epitaxial diamond growth from methane on diamond seed crystals at about 1000.degree. C. in the presence of hydrogen, with pressures from 0.15 to 458 Torr, has been reported. Carbynes (both .alpha. and .beta.) have been produced by oxidizing copper acetylides at atmospheric pressure, followed by acid leaching and a 1000.degree. C. vacuum heat treatment.
The conditions of these processes are such that only limited quantities of the desired product can be produced. Thus, it would be desirable to have a process that operates under more moderate conditions and that can be utilized to produce large quantities of dense carbon in either a batch or a continuous operation.